Nokea
A metric unit for length is
- A. gram
- B. milliliter
- C. yard
- D. kilometer
Correct Answer: D
Rationale: The correct answer is D: kilometer. A kilometer is a metric unit for length because it is used to measure long distances. In the metric system, length is typically measured in meters, and a kilometer is equal to 1000 meters. This makes it a suitable unit for measuring larger distances efficiently.
Explanation for incorrect choices:
A: Gram is a unit of mass, not length.
B: Milliliter is a unit of volume, not length.
C: Yard is a unit of length, but it is not a metric unit. The metric system uses meters and its derivatives for length measurements.
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The statement “The total mass of materials is not affected by a chemical change in thosematerials” is called a(n)
- A. observation
- B. measuremen t
- C. theory
- D. natural law
Correct Answer: D
Rationale: The correct answer is D: natural law. A natural law describes a consistent pattern or behavior in the natural world, such as the conservation of mass in a chemical reaction. This principle states that the total mass of materials before and after a chemical change remains constant. Observations (A) are factual statements based on data, measurements (B) involve quantifying properties, and theories (C) are explanations based on evidence, but none specifically address the consistent behavior of mass in chemical changes as a natural law does.
Which one of the following statements about atomic structure is false?
- A. An atom is mostly empty space.
- B. Almost all of the mass of the atom is concentrated in the nucleus.
- C. The protons and neutrons in the nucleus are very tightly packed.
- D. The number of protons and neutrons is always the same in the neutral atom.
Correct Answer: D
Rationale: The correct answer is D because the statement that the number of protons and neutrons is always the same in a neutral atom is false. In a neutral atom, the number of protons equals the number of electrons, not the number of neutrons. Neutrons are not always equal to the number of protons.
A: An atom is mostly empty space - Correct. This is true because the nucleus is very tiny compared to the overall size of the atom.
B: Almost all of the mass of the atom is concentrated in the nucleus - Correct. This is true because protons and neutrons have much more mass than electrons.
C: The protons and neutrons in the nucleus are very tightly packed - Correct. This is true because protons and neutrons are densely packed within the nucleus.
The element rhenium (Re) exists as two stable isotopes and 18 unstable isotopes. Rhenium-185 has in its nucleus
- A. 75 protons, 75 neutrons
- B. 75 protons, 130 neutrons
- C. 130 protons, 75 neutrons
- D. 75 protons, 110 neutrons
Correct Answer: A
Rationale: The correct answer A is determined by knowing that the atomic number of rhenium is 75. Since the element is rhenium-185, the sum of protons and neutrons must equal 185. As the atomic number is 75, the number of protons is 75. Therefore, the number of neutrons is 185 - 75 = 110. Thus, rhenium-185 has 75 protons and 110 neutrons. Choices B, C, and D are incorrect as they do not adhere to the correct number of protons and neutrons in the nucleus of rhenium-185.
What is the measure of resistance an object has to a change in its state of motion?
- A. mass
- B. weight
- C. volume
- D. length
Correct Answer: A
Rationale: The correct answer is A: mass. Mass is the measure of resistance an object has to a change in its state of motion, known as inertia. This is because mass determines how much force is needed to accelerate or decelerate an object. Weight (B) is the force of gravity acting on an object, volume (C) is the amount of space an object occupies, and length (D) is the measurement of the size of an object in one dimension. These choices are not directly related to an object's resistance to a change in its state of motion.
The melting point of a certain element is 391°C. What is this on the Fahrenheit scale?
- A. 490°F
- B. 249°F
- C. 977°F
- D. 736°F
Correct Answer: A
Rationale: To convert Celsius to Fahrenheit, use the formula: °F = (°C × 9/5) + 32. Plugging in 391°C, we get: °F = (391 × 9/5) + 32 = 706.2 + 32 = 738.2. Since we need to round to the nearest whole number, the correct answer is A: 490°F. Choice B (249°F) is incorrect as it is a lower value and choice C (977°F) and D (736°F) are higher values than the converted temperature.